1. Field of the Invention
The present invention relates generally to a mixing apparatus. More particularly, the present invention relates to a mixing apparatus without extensive external piping to reduce the risk of cross-contamination from one sample to the next.
2. Brief Description of Prior Art
Mixing apparatus have been developed for a variety of special applications to improve the rheological properties of the components being mixed.
Welker Engineering Company, the assignee of the present patent application, has previously produced a prior art crude oil sampler system which includes a crude oil sample container and mixer. Drawings of this prior art apparatus are included in the Information Disclosure Statement filed concurrently with this patent application. As sample accumulates in this prior art sample container, which is at atmospheric pressure, it stratifies according to the specific gravity of the various fluids in the sample. These fluids need to be mixed into a homogeneous composition before a small amount of sample is drawn from the container for laboratory analysis at a location that is typically remote from the crude oil sample container.
In order to circulate the fluids in the prior art crude oil sample container, a mixer is attached to the container. The mixer includes a motor, a pump, and external piping running from the base of the container to the pump and back to the container.
The sample containers in the prior art Welker crude oil sampler system range in size from 2-30 gallons. In the smaller sizes, the external piping is xc2xdxe2x80x3. Larger size containers use larger piping. The volume of fluid in the external piping and the pump varies depending on the size of pipe, but it is a quart of fluid or more.
The external piping runs from the bottom of the container and connects to the suction side of the pump. Additional external piping runs from the discharge side of the pump to the container. On the inside of the container and connected to the external piping is the mixing pump return. (Also sometimes called a down comer).
The down comer is an elongate piece of pipe with a plurality of holes in the sides to spray the fluid back into the sample container. The down comer has a plug in the end, which also has several holes so fluid can sweep the bottom of the container.
Before a sample is drawn for laboratory analysis, the prior art mixer is turned on to circulate the fluids in the sample container. As the fluids are circulated they become more homogenous. The International Standards Organization (ISO-3171) recommends that crude oil be circulated at a rate of one volume of the sample container per minute before a sample is drawn.
The gravity of fluids placed in the sample container may vary from APIxc2x08 to 45. Depending on the gravity of the crude oil, and ambient conditions, a heat blanket may first be placed on the sample container before circulation is attempted. Circulation of the fluids in the sample container may last for up to 45 minutes depending on the circumstances, but a typical mixing time is about 15 minutes.
After the fluids have been circulated and the sample has been drawn it is time to clean up. To clean the prior art sample container and purge the external piping and pump, the crude oil is first pumped out. An inert fluid, such as kerosene, is then pumped into the sample container and circulated. The dirty inert fluid is then pumped out. Clean inert fluid is then pumped into the sample container and circulated. The dirty inert fluid is then pumped out. The container is opened and wiped out and the external piping is drained. After the container is closed, it is ready for the next sample. The amount of time it takes to clean the system varies, depending on the size, but a typical clean up time is about 20 minutes. Sometimes operators cut corners and this purging process does not completely clean out the external piping or pump, which can lead to cross-contamination. There is a need to reduce or eliminate the external piping to and from the pump to reduce the chance of cross-contamination.
In an alternative embodiment of the prior art crude oil sample container, a spray nozzle is located in the sample container instead of the down comer. This alternative embodiment likewise had external piping connecting the sample container and the pump. Because of the external piping, this alternative embodiment also has the potential problem of cross-contamination.
Another prior art apparatus produced by Welker is the constant pressure crude container. This apparatus contains several gallons of liquid and also includes a mixer. Drawings of this prior art apparatus are also included in the Information Disclosure Statement filed concurrently with this patent application. A sliding piston divides the constant pressure crude container into a pressurized precharge end and a sample end.
Pressurized gas in the precharge end is utilized to maintain a pressure on the sliding piston. The piston transfers pressure to the sample components to prevent vaporization loss. Sample components are drawn from the sample end of the container through external pipes to the pump, where they are forced through external pipes back to the container and are sprayed through small orifices resembling a showerhead on the sample side of the piston.
The prior art constant pressure crude container, like the crude oil sample container needs to be cleaned and the external piping and the pump must be purged after each use. Failure to properly clean and purge can lead to cross-contamination of the next sample by the prior sample.
The type of pump used in these prior art devices is primarily a matter of manufacturing choice. In the prior art crude oil sampler systems Welker Engineering Company has used a model 2S rotary gear pump with helical gears from Brown and Sharpe of North Kingston, R.I. This pump produces about 9 gpm at 1750 rpm. The model 2S pump from Brown and Sharpe is also used in the 0-200 psi prior art constant pressure crude containers. In prior art constant pressure crude containers with higher pressure ratings a series 5K model 67-L-3461 magnetic drive gear pump from Micropump of Vancouver, Washington is used. The Micropump apparatus is rated at about 5 gpm at 1750 rpm with a 100 psi differential. Regardless of what type of pump is used, the external piping and pump still needs to be purged. There is a need to reduce or eliminate the external piping to and from the pump to reduce the chance of cross-contamination.
U.S. Pat. No. 5,005,982 (Kistner) discloses rotatably mounted intermeshing gears in a chamber between an inlet for introducing components therein and an outlet for discharging components therefrom, wherein the rotating gears shear and extrude the components passing between the gears. Kistner teaches a material processor, using rotating gears having intermeshing teeth, for improving the rheological properties of the components being mixed. The Kistner device is designed to crush and mix the components passing through the rotating gears by providing several different clearances between slowly moving processor teeth. The components being mixed are sheared and extruded as they pass between the teeth before being discharged. The increased clearances between the processor teeth required to crush larger particles, however, limit the Kistner device to rotating the intermeshing gears at speeds that would allow the driven gear to be forced ahead and out of contact with the drive gear by the material therebetween. This typically requires the gears to be rotated at relatively slow speeds. The slow-rotating intermeshing gears provide minimal velocity to materials being discharged from the outlet.
U.S. Pat. No. 2,995,774, issued to Pasquetti, discloses another mixing apparatus. The Pasquetti apparatus is used for thick masses. It utilizes at least two screw-like intermeshed blades mounted on parallel shafts, for effecting an overall movement of material parallel to the screw-like blades. The material is thus alternately placed under high pressures and then forced into thin layers which move along the screw-like blade before being discharged.
Although the apparatus of Kistner and Pasquetti and the two prior art Welker devices achieved some degree of circulation of the fluid, a better mixer is still needed. In addition, mixing devices utilizing remote pumps and piping must be drained and flushed after each use in order to avoid cross-contamination by residual components within the pipes.
A need exists for an apparatus that eliminates external piping from a container to a pump. Such an apparatus would be particularly useful to avoid cross-contamination of batch samples such as those taken in the oil industry. There is also a need in some circumstances for a faster mixer.
In the oil industry batch sampling is common. Periodically small samples (for example 20 cc. each) of fluids are put into a holding container. These liquids tend to stratify over time. Before taking a sample back to the laboratory for analysis, it is best to mix fluids to achieve a homogenous sample. As each small sample is hoped to be representative of a large volume of fluid, homogenization and minimization of contamination are significant concerns. The present invention does not require external piping to transfer components to the mixing pump and back to the container. Because there is no external piping to the pump, the present invention minimizes the possibility of cross-contamination. The present invention directs the fluid entering the pump intake and exiting the pump outlet so that a mixing turbulence is created within the material container, in addition to the mixing action of the intermeshing gears within the pump. The present invention appears to mix stratified fluids more quickly and more thoroughly then prior art devices. Clean up of the present invention will also be shorter.